This invention relates generally to xerographic copying methods and apparatus, and more particularly, it relates to the heat and pressure fixing of particulate thermoplastic toner by direct contact with a heated fusing member.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing of the image thereto in one of various ways, for example, as by heat and pressure.
In order to affix or fuse electroscopic toner material onto a support member by heat and pressure, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky while simultaneously applying pressure. This action causes the toner to flow to some extent into the fibers or pores of support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy and pressure for fixing toner images onto a support member is old and well known.
One approach to heat and pressure fusing of electroscopic toner images onto a support has been to pass the support with the toner images thereon between a pair of opposed roller members, at least one of which is internally heated.
As the copy sheet passes out of the nip formed by the fuser roll and the back-up roll, it is necessary to provide means such as an air stripper, stripper blades, finger-like members or other suitable sheet separating means to insure that the copy paper proceeds along a predetermined path from the nip formed between the fuser roll and back-up roll to a conveyor belt or the like for moving the copy paper towards the exit of the machine or apparatus in which the fuser is employed.
In a soft roll fuser where the silicone rubber or other such material forming the outer surface or layer of the fuser roll is relatively (i.e. 50 mils or greater) thick an air stripper is used to assist self-stripping which is brought about by the flexing of the rubber as it moves through the nip area. Where the outer surface is relatively thin an air device is the primary stripping mechanism. Air or noncontact stripping is preferred for use with a soft roll fuser because the soft surface can be easily damaged by conventional contact stripper fingers. However, air stripping is a relatively costly addition to a copier or duplicator machine where the machine does not have an existing air compressor which could be employed for this additional function. Some machines have been known to utilize an air compressor for effecting pressure engagement of fuser rolls. In such a machine the incremental cost of air stripping would be acceptable.
In a machine having a soft fuser and a contact stripper special care must be taken in the structuring of the stripper mechanism such as fingers in order to prevent or minimize damage to the soft roll surface. Damage from the stripper fingers can occur when there is a misstrip. A misstrip takes place when the force required to strip a toner laden sheet from the fuser roll exceeds the force available with the stripper finger structure used. Very often due to a misstrip, the paper forces the fingers to gouge the soft surface of the roll.
Prior art sheet removal devices are known which are designed to preclude or minimize the damaging of fuser roll surfaces. One such device is illustrated in U.S. Pat. No. 3,844,252 and comprises a finger structure having a tip portion which rides on the surface of the fuser roll and acts to remove the sheets therefrom. The opposite end of the finger is bifurcated for receiving a spring clip. The clip adjacent the open end of the bifurcated area has a pair of detents for receiving a pivot pin on which the finger is mounted. The rest of the clip comprises an open area into which the pivot pin can move as will be explained hereinafter. Upon the occurrence of a sheet misstrip or jam condition, whereby the finger is caused to exert undue pressure against the roll surface, the finger is forced back against the holding pressure of the pivot pin with sufficient pressure to cause the pin to be released from the detent and move into the open area thus allowing the finger to move away from the fuser roll. The finger is thus permitted to fall away from the roll surface to an inoperative position.
Stripper fingers such as those described in the above-mentioned patent work quite well in minimizing fuser roll damage. However, such stripper fingers require resetting, usually by a qualified technical person. Simply clearing the paper jam by removal of the misstripped sheet by a non-technical person will not render the machine operative again.
Accordingly, it is intended by means of the present invention to provide an improved contact sheet removal apparatus or guide comprising one or more stripper finger structures for use with a soft roll fuser which minimizes the hazard of damage to the soft outer layer of the fuser roll because under adverse conditions it is deflected out of contact with the fuser roll surface. The finger structure is designed to be readily repositioned to an operative position after the removal of a misstripped sheet of paper.